The present invention relates to a power supply circuit for an image display apparatus. More particularly, the present invention relates to a technique for preventing leakage of electromagnetic waves generated in the apparatus to the outside of the apparatus.
Conventionally, electronic apparatuses have been requested to comply with the requirements of the EMC (Electromagnetic Compatibility) standards, i.e., the EMI (Electro Magnetic Interference) measures for preventing unintended emission of electromagnetic waves and the EMS (Electro Magnetic Susceptance) measures for preventing malfunction upon reception of electromagnetic waves. In Japan, the VCCI (Voluntary Control Council for Interference by Information Technology Equipment) was established and self-imposed regulations are conducted based on recommendations of the CISPR (International Special Committees on Radio Interference). This also applies to the U.S. and Europe. Image display apparatus, such as a display apparatus with a plasma display panel, are subjected to the regulations since they generate electromagnetic waves from a display unit such as a plasma display panel. The regulations demand that leakage of the electromagnetic waves to the outside of the apparatus be reduced to a predetermined level. A power supply unit of the apparatus is one of paths which electromagnetic waves leak to the outside. Since electromagnetic waves leak to the side of a commercial power supply, etc. through a power cord or the like, measures are taken so that electromagnetic waves are attenuated by a filter circuit in the power supply unit.
FIG. 6 is a schematic diagram showing a circuit configuration of a conventional display apparatus with a plasma display panel. The circuit shown in FIG. 6 comprises: a power supply circuit including a circuit board 13a1′ with a power cord 30′ directly connected thereto and a filter circuit A′ formed thereon which includes an inductance element; a circuit board 13a2′ with a fuse 60′ connected thereto and a filter circuit B′ formed thereon; and a circuit board 13a3′ with a switch circuit formed thereon which switch on/off the connection between the fuse 60′ and the filter circuit B′. The circuit shown in FIG. 6 further comprises: a circuit board 13b′ with a power supply unit S′ formed thereon which includes a filter circuit C′ with inductance elements connected thereto; a circuit board 12a′ with a drive circuit D1′ formed thereon which drives a plasma display panel 11′ as a display unit based on an image signal; a circuit board 12b′ with a drive circuit D2′ formed thereon; and a rear cover 16′ for covering the rear side of the display apparatus.
FIG. 7 is a diagram showing an example of the configuration of a display apparatus with a plasma display panel using the circuit shown in FIG. 6. In FIG. 7, a retaining fitting 14′ for retaining a circuit boards 13a1′, 13a2′ and 13a′, a circuit board 13b′, and circuit boards 12a′ and 12b′ are arranged between the plasma display panel 11′ and the rear cover 16′. A front filter 15′ is arranged at the front of the plasma display panel 11′. In the above configuration, electromagnetic waves in the power supply circuit and the power supply unit S′ shown in FIG. 6 are attenuated by use of filter circuits A′, B′ and C′.
One of conventional arts relevant to the present invention is described, for example, in Japanese Patent Laid-open No. 2004-29264. This patent gazette describes a configuration in which a noise filter circuit installed at the rear side of a plasma display panel is covered by a cover of magnetic metal material and a portion of the cover close to the noise filter circuit is secured to a chassis member in order to provide a plasma display apparatus which does not generate audible noise sound.
Japanese Patent Laid-open No. 2004-29264